1. Field of the Invention
The present invention relates to a method for the production of tissue paper and, more particularly to a method for the production of a pulp suspension for use in the production of tissue paper.
2. Description of the Related Art
Tissue paper ideally displays a high absorbency and a high water absorption capacity coupled with a high tear resistance. The absorbency and water absorption capacity are defined essentially by the volume and porosity of the tissue paper. To increase the volume it was already proposed in the prior art in WO 03/062528 to press the tissue paper web during production only on a zone basis in order to obtain only slightly pressed or unpressed voluminous regions and pressed regions of greater tear resistance.
The porosity, the permeability, the absorbency and the dewaterability of the tissue paper are co-defined, essentially by the refining degree of the fibers in the pulp suspension from which the tissue paper is produced. Here a high refining degree gives rise to a high fines content in the suspension, leading to a low porosity and permeability of the produced tissue paper web.
On the other hand the tear resistance is co-influenced by the refining degree of the fibers in the pulp suspension such that the tear resistance is increased by increasing the fines fraction. Hence the requirements imposed on the tear resistance conflict with the previously mentioned requirements imposed on the water absorption capacity, the absorbency and the dewaterability. Further, to save production costs it is desirable to use old paper instead of cellulose, at least in part, in the production of tissue paper.
Experience indicates that a pulp suspension made from treated old paper has a higher refining degree and hence a larger fines fraction, so the opinion in the prior art was that old paper is ill-suited for producing tissue paper, in particular tissue paper with a high water absorption capacity and high absorbency (so-called bulky tissue).
What is needed in the art is a method for the production of a tissue paper web, with which it is possible to produce tear-resistant tissue paper with a high water absorption capacity and absorbency from a pulp suspension with old paper.